This is a continuation of a comprehensive investigation of the endocrine physiology of egg maturation in mosquitoes. This information will also provide the background required for our studies on the role of the endocrine system in mosquito behavior. To date, egg maturation has been the principal criterion for determining when the corpora allata are secreting hormone and when the medial neurosecretory cells (MNC) of the brain produce and release their hormone from the corpus cardiacum. In this proposal, experiments related to egg maturation have been planned: 1) to provide more information on the storage of egg development neurohormone through bioassay of corpora cardiacia, 2) to establish what type of signal comes from a blood meal to the corpus cardiacum to initiate release of neurohormone, and 3) to investigate the influence of the ovary itself on the other parts of the endocrine system. In related endocrine studies we intend: 1) to investigate further the effect of the MNC and the corpora allata on triglyceride and glycogen metabolism, 2) to determine the source of the inhibitor of yolk deposition produced by ovaries retaining mature eggs, 3) to show whether biting behavior of Culex females, exposed to low-temperature and short-days, is mediated by a hormone, and 4) to observe the ultrastructural changes in neurosecretory neurons when egg development neurohormone is being released. Mating behavior will be studied in species which only mate in reduced light (e.g. Anopheles and Culex) to establish the age at which copulation results in insemination.